I looked at your picture and it appears you can just use the pot to control motor speed.

PWM is just a way of providing a variable (average) DC without the usual series pass transistor power wasting heat. It's a variable duty cycle series of pulses, in this case at a 21 KHz rate.

I have worked extensively with PWM to control loco motor speed. What do you need to know?

If you want to learn more about PWM, just google it and there is endless info with as little or as much theory as you can stomach.  All modern toy trains with DC motors use PWM for electronic speed control.

You will definitely be able to use this for train animation.  The 21 kHz is fine and will not be an issue for a layout animation.  The curious thing about your module is it can only be adjusted down to 5%?  In other words you cannot turn it "off" by turning the knob all the way to one side.  That seems a little odd.  So while the motor may not spin at such a low setting it will just waste power.  But I see they go for less than $4 shipped so it's a good value in any event.

If the stated 3 Amp rating is accurate, that should drive most animation DC motors.  I tried a couple of the eBay listings but none had a schematic like some listings do for these eBay modules.  When the time comes to animate something, if you do come across the schematic post it along with what you're trying to do.  As I've said before you have to take some of the "specifications" for these insanely priced eBay modules with a grain-of-silicon (salt).

Oh, and if it's a question of value, note that in many cases you can simply use one of those DC-DC LM2596 regulator modules (99 cents or so) to drive a DC animation motor.  The nice thing about your module is the "large" easy to use knob rather than a tiny screwdriver adjustment.

Finally, call me picky, but the term "motor speed controller" can be deceptive.  Yes, these modules can "control" the speed of a motor but not fixed speed.  You are the controller by turning the knob.  If you load the motor at a given setting, the motor slows down.  This is like calling the train transformer a "speed controller" in a conventional engine (without speed control).  To actually control (constant speed around curves, grades, additional cars, etc.) the motor you need some kind of feedback...whether from a tachometer or other sensor.  I'm pretty sure this module does NOT handle that. 

Thanks Stan. As usual, you are incredibly helpful. When I get ready to play I'll come back to this topic.

Bob, if I knew anything about PWM, I could come up with an intelligent question. I guess my main (un-intelligent) question is: Is PWM just adjustable (duration & freq.) square wave DC, and as such would not work trying to drive AC motors (and I'm not much on motors either), but would work fine on any (or most) DC motors?

Most of the AC motors in our toy trains are actually series wound universal motors. That means they will run on AC or DC.

PWM can be used for AC motors, at least the folks at Freescale think so.

PWM Control of the Single-Phase A.C. Induction Motor

I've never had the need, but I use PWM to control the motor speed of the DC smoke fan motor on the Super-Chuffer.  PWM means Pulse Width Modulation, and normally it has a fixed frequency and just varies the pulse width (on/off) duration of the waveform driving the device.  Sometimes, pictures help, note the frequency stays the same, but the duration of the on cycle changes.

Roy & Gunner,

Thank you for the information. That makes much sense and helps a lot.

PWM does work with AC induction motors just fine, but requires a little bit more electronics.  The controller needs to read the AC sine wave to start it's cycle at the exact point when the wave crosses over zero.  It is both more and less complex than it sounds.  

As far as the motors in our trains are concerned, the others are correct these will run on either AC or DC just fine.  In some experiments, however, I couldn't get useful results driving a post war loco with a PWM driver.  Under about 75% duty cycle the motor would stall, and performance wasn't particularly good until somewhere around 90%, making it fairly useless for speed control.  This is based off of some rough experiments, and I've had a few ideas on how to fix the problem, just haven't had time to work with it lately.  

Plenty has already been posted. The PWM module in your photo is a moderate power unit judging by the small output transistor on the PC board. It would probably work well with a simple animation setup. An adjustable voltage regulator IC would work as well and would be a simpler circuit. For running locos with two or more DC can motors, I've used higher power PWM modules with heat sunk output devices. These are very efficient and provide very smooth speed control. Even the higher power units are very inexpensive ($5-$15) and available in many places.

Thank you John & Bob for the information. It helps a lot with my understanding of PWM.